Port always shows up, it doesn't bug out. That's just the port Blockland is trying to use, not what it is using.
Also, LAN doesn't require port forwarding AFAIK so it always shows there.
Weird how it shows up in the server list and is unjoinable, though. Seems like this is another case of "--- ping". I've heard that's because you didn't port forward properly.
There's plenty of people who have had this same problem, hopefully one comes to show the solution.